1. Technical Field
Example embodiments of the present invention relate to a semiconductor device and method of fabricating the same, and more particularly to a semiconductor device including a higher resistivity region and method of fabricating the same.
2. Discussion of the Related Art
Unlike volatile memory devices, non-volatile memory devices may retain data stored in memory cells when its power supply is turned off. Non-volatile memory devices may be used in various electronic applications (e.g., computers, mobile communication systems, memory cards, etc.).
Flash memory devices may represent a class of non-volatile memory devices. Flash memory devices may include memory cells with a stacked gate structure. The stacked gate structure may include a tunnel oxide layer, a floating gate, an inter-gate dielectric layer and a control gate electrode. Each of the tunnel oxide layer, floating gate, inter-gate dielectric layer and control gate electrode may be stacked on a channel region. The reliability and efficiency of flash memory devices may increase by increasing a film quality of the tunnel oxide layer and/or a coupling ratio of the memory cells.
Another example of a non-volatile memory device may be a phase-change memory device. Phase-change memory devices may include a phase-change material capable of writing and/or erasing data. A unit cell of the phase-change memory device may include an access element and a data storage element serially connected to the access element. The data storage element may include a lower electrode electrically connected to the access element and a phase-change material layer in contact with the lower electrode.
The lower electrode may function as a heater (e.g., due to a higher conductivity or a lower resistivity). When a write current flows through the access element and the lower electrode, a given amount of heat, which may be interpreted in joules, may be generated between the phase-change material layer and the lower electrode. The given amount of heat may change the structure of the phase-change material layer into another type (e.g., an amorphous structure, a crystalline structure, etc.). The term “phase-change” may refer to any detectable change between two structures (e.g., between a fully crystallized structure and a fully amorphous structure). The phase-change material layer may include different electrical characteristics based on its structure. For example, an amorphous structure may include a higher resistance as compared to a crystalline structure.
A conventional phase-change memory device may require a higher current (e.g., a write current) in order to cause a phase-change (e.g., as compared to other devices). The size of address lines and/or an access device to transfer the current to each cell may be limited because of the heat induced by the higher current. The limited size and/or increased heat characteristics may increase the difficulty of integrating phase-change memory devices (e.g., into a larger semiconductor device). The higher current may be reduced by reducing a contact area between the lower electrode and the phase-change material layer. A transition metal (e.g., titanium, a nitride compound, etc.) may be used for the lower electrode. However, if the lower electrode includes a higher thermal conductivity, the lower electrode may function as a heat sink, and a phase change may be more difficult to detect.
Other lower electrodes may include a metal compound (e.g., metal nitride, refractory metal nitride, metal silicon nitride, refractory metal silicon nitride, etc.) having a higher resistance (e.g., as compared to titanium and/or the nitride compound). However, if the lower electrode includes a metal compound having a higher resistivity, a parasitic resistance of the lower electrode and a power level required to store data in the phase-change memory cell may be increased.